Conventionally, drive assist technologies such as disclosed in Patent Documents 1 to 6 have been proposed in each of which a roadside apparatus provides information required by a vehicle to drive safely to an in-vehicle apparatus, and the in-vehicle apparatus assists the vehicle to drive based on the provided information.                Patent Document 1: JP-2001-23098 A        Patent Document 2: JP-2001-101599 A        Patent Document 3: JP-2001-167387 A        Patent Document 4: JP-2001-319295 A        Patent Document 5: JP-2004-38244 A        Patent Document 6: JP-2006-236094 A        
The roadside information provided by the roadside apparatus includes information on an obstacle which cannot be sensed or viewed by various sensors (hereinafter referred to as autonomous sensors) mounted in the vehicle. Therefore, the use of such roadside information by the vehicle operator allows an early risk determination to be made for an obstacle or the like present around the vehicle but not viewable from the vehicle.
However, the roadside information has the possibility of being “spoofing” information and the accuracy of the roadside information (e.g., the accuracy of obstacle detection) is unknown to the vehicle operator. Accordingly, the reliability of the information is generally low compared with information provided by the autonomous sensors.
That is, compared with the information provided by the autonomous sensors, the roadside information allows an early risk determination, but the reliability thereof is low. On the other hand, the information provided by the autonomous sensors is higher in reliability than the roadside information, but it does not allow an early risk determination.
Thus, the roadside information and the information provided by the autonomous sensors have their respective advantages and disadvantages so that an in-vehicle drive assist system which allows an early risk determination has been in demand.